“A book is a gift you can open again and again.” –Garrison Keillor–

Climate is not the same as weather. It is long term, whereas weather is short term, like today, or this week.
Climate is a large, complex system which, like any system, can be affected by different things. By pushing more greenhouse gases into the atmosphere and so trapping heat which would otherwise escape into space, by doing this, we are pushing more energy into the system, and our climate produces weather patterns according to how much energy is in the system. This disturbs weather patterns, meaning we get hotter, drier, wetter, windier weather in different places at different times to usual.

Land-use change, such as deforestation, is a big contributor because trees are essentially ‘wet sticks of carbon’, and so burning them both releases CO2 and prevents the trees from absorbing CO2 through photosynthesis, their method of turning sunlight, nutrients and water into energy to grow.
Burning fossil fuels for energy – coal, oil and gas – is a major contributor, as is industrial agriculture, from use of carbon-based pesticides and fertilisers, and fuel for tractors etc. These inputs are avoided in organic agriculture.
So, many human processes increase the amount of greenhouse gases discharged into the atmosphere, and many others remove the earth’s natural ability to absorb them.